Fix ACP reconnect fallback for internal session-not-found errors

[dutifulbob]

Summary

• fix reconnect recovery when ACP adapters return -32603 Internal error with session-missing details in error.data
• improve reconnect load strategy to try agentSessionId first, then fallback candidates, before creating a new session
• add regression coverage for both error classification and reconnect behavior

What changed

• src/error-normalization.ts
  • expanded resource-not-found detection to include nested ACP data fields (for example data.details: "Session not found")
• src/session-runtime.ts
  • added load-session candidate resolution (agentSessionId, then sessionId)
  • retries load across candidates on recoverable not-found errors
  • falls back to createSession only after candidates are exhausted
• test/mock-agent.ts
  • added test flags to emulate load-session internal-not-found error shapes and required load target IDs
• test/error-normalization.test.ts
  • regression test for -32603 + data.details: Session not found
• test/cli.test.ts
  • regression test: prompt falls back to new session on internal-not-found load errors
  • regression test: prompt prefers agentSessionId on reconnect load

Verification

• npm test
• npm run lint
• npm run typecheck
• npm run format:check
• manual smoke (real Claude adapter):
  • command: timeout 45 node dist/cli.js --approve-all --timeout 120 --format text claude -s oc-claude-smoke "Reply exactly FIX_OK"
  • output contained FIX_OK and [done] end_turn (previously this path failed with Internal error / Session not found)